For the core material of a motor, in the past, those obtained by laminating the flat rolled magnetic steel sheets, electrical steel sheets and the like were used, however, in recent years, the powder magnetic core has come to be utilized. Because the powder magnetic core is manufactured by compressively forming the powder for a powder magnetic core, the degree of freedom of the shape is high, a core of a three-dimensional shape can be easily manufactured, and therefore reduction of the size and reduction of the weight of the motor is easier compared to the motors of prior arts.
With respect to the powder magnetic core used for the electromagnetic parts, it is important to be excellent in handling performance in the manufacturing step, and to have sufficient mechanical strength so as not to be broken in winding for forming a coil. Considering these points, a technology for coating the iron powder with an electrical insulating material in manufacturing the powder magnetic core is known. More specifically, because the iron powder is coated with the electrical insulating material, the iron powder particles are adhered to each other through the electrical insulating material, and therefore the mechanical strength of the powder magnetic core obtained using the iron powder coated with the electrical insulating material improves more than that of the powder magnetic core manufactured using the iron powder as it is without coating.
With respect to the technology for increasing the mechanical strength of the powder magnetic core, Patent Literatures 1 and 2 are known. Out of these technologies, in Patent Literature 1, a technology is disclosed in which the mechanical strength of the powder magnetic core is increased by coating the surface of the soft magnetic powder particles with a glass-like insulating layer obtained from phosphoric acid and the like and further coating the same with a resin layer formed of an epoxy resin, imide resin, or fluorine contained resin. Also, in Patent Literature 2, it is described that, when the powder for a powder magnetic core in which a phosphoric acid-based chemical conversion coating and a silicone resin coating containing predetermined elements are formed in this order on the surface of the iron-based soft magnetic powder particle is used, a powder magnetic core satisfying such properties of high magnetic flux density, low iron loss, and high mechanical strength is obtained.